FIG. 5 is a partial cross-section view of prior art four-pass torque converter 200. Torque converter 200 includes cover 202 arranged to receive torque, impeller 204 with impeller shell 206, turbine 208 with turbine shell 210, hub 212, and lock-up clutch 214 with piston plate 216. Torque converter 200 includes pressure chambers 218 and 220. Chamber 218 is bounded by hub 212, piston plate 216, and seal plate 222. Chamber 220 is bounded by cover 202, hub 212, and piston plate 216. To close clutch 214 (non-rotatably connect cover 202 and piston plate 216), fluid pressure in chamber 218 is increased and fluid pressure in chamber 220 is decreased to displace piston plate 216 in axial direction AD1. To open clutch 214, fluid pressure in chamber 220 is increased and fluid pressure in chamber 218 is decreased to displace piston plate 216 in axial direction AD2.
End E of seal plate 222 is butt-welded to hub 212 with weld 224. Root 226 for weld 224 is an area of weld 224 most susceptible to failure in response to pressure applied to seal plate 222 during the close mode for clutch 214. For example, simulations have shown that for a fluid pressure of 9.5 bar in chamber 218, the stress (tension) on root 226 is greatly elevated. An axial extent of weld 224 is linked to thickness 228 of plate 222. For example, weld 224 extends no further than seal plate 222 in direction AD1.